fix(common): drop OpenAI itemId from provider options

[zwpaper]

Notes for reviewer

Fixing error:

Chat and stream with openai gpt codex works:

Learn from:

• discuss: gpt-5-codex failure: AI_APICallError: Item 'rs_... of type 'reasoning' was provided without its required following item. anomalyco/opencode#2941
• commit: anomalyco/opencode@40836e9

in the commit comment, it also says codex also did this patch.

related discuss:

• Item 'rs_...' of type 'reasoning' was provided without its required following item vercel/ai#7099

Summary

• strip OpenAI itemId fields from providerOptions on message parts
• keep formatted/stored messages aligned with schema validation

Test plan

• Not run (not requested)

🤖 Generated with Pochi

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 18.44%. Comparing base (e83a010) to head (1ea828a).
⚠️ Report is 63 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1164      +/-   ##
==========================================
+ Coverage   18.42%   18.44%   +0.01%     
==========================================
  Files         626      626              
  Lines       56626    56641      +15     
  Branches     1381     1385       +4     
==========================================
+ Hits        10431    10445      +14     
- Misses      45955    45956       +1     
  Partials      240      240              

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